1. Field of the Invention
The present invention relates to thyristors in general, and, in particular, to a new and useful gate turn-off thyristor comprising four layers of alternating conductivity type.
2. Description of the Prior Art
Thyristors with a p-doped control base layer are already known, which can be turned off by means of a negative control current flowing over the control base terminal (Semiconductor Power Converter International Conference Mar. 23-25, 1977 (IEEE), Orlando, Fla. "The current status of the power gate turn-off switch (GTO) p. 39-49). In order to positively turn off the tryristor, this control current must be about 20 to 30% of the load current to be turned off. Furthermore, a turn-off voltage is required which is between -10 V and -70 V. Turning off the thyristor requires thus a power circuit-fed control current generator with a load switch which requires considerable engineering costs.
A possibility of reducing these costs resides in increasing the turn-off gain (ratio of load current to turn-off current). Turn-off thyristors with a relatively large turn-off gain (.gtoreq.5) cause, however, considerable on-state power losses, so that a high turn-off gain is foregone and the high engineering costs for the turn-off control are accepted.
A thyristor is already known which can be turned off by means of an integrated field effect transistor part, that bridges the cathode-emitter junction of the thyristor (DOS No. 26 25 917). But only relatively small currents can be conducted over this field effect transistor part, and only relatively small load currents can be turned off. The on-state behavior of the field effect transistor part is also very unfavorable.